Simultaneous voltammetric determination of heavy metals by use of crown ether-modified electrodes and chemometrics

A three-sensor array consisting of a graphite-epoxy composite electrode (GEC), 4-carboxybenzo-18-crown-6-GEC and 4- carboxybenzo-15-crown-5-GEC was employed for the simultaneous determination of Cd(II), Pb(II) and Hg(II) by differential pulse anodic stripping voltammetry (DPASV). Sensors were firstly studied for the determination of Hg(II); secondly, peak current responses confirmed that all sensors showed differentiated response for the three considered metals. A response model was developed to resolve mixtures of Cd(II), Pb(II) and Hg(II) at the μg L⁻¹ level; Discrete Wavelet Transform was selected as preprocessing tool and artificial neural network used for the modelling of the obtained responses

Electrocatalytic Determination of Vitamin C Using Calixarene Modified Carbon Paste

Abstract Effect of in situ complexation of some ions with variable valencies, like Co(II), Ni(II), Mn(II), Cu(II) and Pb(II) on the the electrooxidation of Vitamin C (l-ascorbic acid) was studied by cyclic voltammetry using carbon paste electrodes modified with p-tert-butylcalix Keywords: Carbon paste electrode, Calixarene, Ascorbic acid, Voltammetry Vitamin C (l-ascorbic acid), a water-soluble vitamin that is widely required for metabolism and consumed on a large scale is electroactive and has been studied extensively [1 -4]. Several chemically modified electrodes (CMEs) have been fabricated, and ascorbic acid has been used as a model compound to study the effect of modification, which in-turn have led to a number of electrochemical sensors. CMEs based on enzymes [5 -7], polymerization [8 -13], dyes [14 -17], self assembled monolayers [18 -21], redox [22 -23] and macrocyclic complexes of transition metal ions are reported. Most of the macrocyclic complexes used as modifiers are phthalocyanines [24 -26], porphyrins [28 -29] or cyclam type of molecules A reaction at an electrode is said to be electrocatalytic if the oxidation/reduction potential is decreased considerably and if there is a simultaneous increase in peak currents. The oxidation of ascorbic acid (AA) was studied in 0.01 M perchloric acid (pH 2.0), 0.04 M acetic acid (pH 3) and ammonium acetate media (pH 5.1) containing Cu(II), Co(II), Ni(II), Mn(II) and Pb(II) ions using plain carbon paste electrodes (PCPEs) and modified carbon paste electrodes (MCPEs). Electrocatalytic activity was observed only for the MCPEs in ammonium acetate media containing Pb(II) ions, which is consistent with previous observation that the uptake of lead ions is favored in ammonium acetate mediu

DISCOVERY OFRANKINGFRAUD FOR MOBILE APPS

Ranking fraud in the mobile App market refers to fraudulent or deceptive activities which have a purpose of bumping up the Apps in the popularity list. It becomes more and more frequent for App developers to use shady means such as inflating their Apps’ sales or posting phony App ratings to commit ranking fraud. While the importance of preventing ranking fraud has been widely recognized. There is limited understanding and research in this area. In this project, we provide a holistic view of ranking fraud and propose a ranking fraud detection system for mobile Apps. We investigate two types of evidences i.e. ranking based evidences, rating based evidences by modelling Apps’ ranking and rating behaviours through statistical hypotheses tests. We evaluate the proposed system with real-world App data collected from the App Store for a long time period. In the experiments we validate the effectiveness of the proposed system and show the scalability of the detection algorithm as well as some regularity of ranking fraud activitie

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Abstract The feasibility of fabricating copper-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and in 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The electrodes so formed were able to bind Cu(II) ions chemically and gave better voltammetric responses than the unmodified ones. The crown ethers studied and compared were 15-crown-5, benzo-15-crown-5 and dibenzo-18-crown-6. With a 3% benzo-15-crown-5 CME, Cu(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.05 ppm. By differential pulse anodic stripping voltammetry Cu(II) could be quantified over the range 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Fe(II), etc. have also been studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages

Bevacizumab in choroidal neovascularization secondary to Indian tick typhus: A rare case report

Tick typhus causes hemorrhagic lesions over the skin. Retina also shows hemorrhages and exudates. Many cases have been reported in western literature about this condition. To our best of knowledge, this is the first case report of tick typhus in India which was also associated with inflammatory choroidal neovascularization

Electrochemical behaviour of some copper(II) salts in 20 wt.% propylene carbonate'/ ethylene carbonate: Standard potential of the Cu 2' /Cu system at 25 8C

Abstract The behaviour of Cu(ClO 4 ) 2 , CuCl 2 and CuBr 2 in 20 wt.% propylene carbonate (PC)'/ethylene carbonate (EC) has been studied by conductivity, potentiometry and voltammetry. The conductance behavior of copper(II) halides in 20 wt.% PC'/EC is explained on the basis of the equilibrium 3CuX 2 X/Cu 2' '/2CuX 3 and 2CuX 2 X/(CuX 2 ) 2 . A copper indicator electrode in conjunction with a Hg/HgCl 2 (s) in 20 wt.% PC'/EC reference electrode was used for the potential measurements. The results of the potentiometric measurements, combined with those of the conductance measurements, provided the standard potential, E 8, of the reaction Cu 2' '/ 2e ( X/Cu(s) versus SHE in 20 wt.% PC'/EC at 25 8C, which is found to be 0.4009/0.002 V. Sampled dc and cyclic voltammetric measurements were also undertaken with these Cu(II) salts in 20 wt.% PC'/EC using Pt working and counter electrodes and Hg/ HgCl 2 (s) in 20 wt.% PC'/EC as the reference electrode. These voltammetric measurements yielded the standard potential value (0.3949/0.003 V vs. SHE) of the system, which is in agreement with the value obtained by the potentiometric method.

Discovery Ofrankingfraud For Mobile Apps

Ranking fraud in the mobile App market refers to fraudulent or deceptive activities which have a purpose of bumping up the Apps in the popularity list. It becomes more and more frequent for App developers to use shady means such as inflating their Apps' sales or posting phony App ratings to commit ranking fraud. While the importance of preventing ranking fraud has been widely recognized. There is limited understanding and research in this area. In this project, we provide a holistic view of ranking fraud and propose a ranking fraud detection system for mobile Apps. We investigate two types of evidences i.e. ranking based evidences, rating based evidences by modelling Apps' ranking and rating behaviours through statistical hypotheses tests. We evaluate the proposed system with real-world App data collected from the App Store for a long time period. In the experiments we validate the effectiveness of the proposed system and show the scalability of the detection algorithm as well as some regularity of ranking fraud activitie